Geothermal fluids from hot springs and wells have been sampled from a number of locations, including: 1) the North Island of New Zealand (three sets of samples from three different years) and the South Island of New Zealand (1 set of samples); 2) the Cascades of Oregon; 3) the Harney, Alvord Desert and Owyhee geothermal areas of Oregon; 4) the Dixie Valley and Beowawe fields in Nevada; 5) Palinpiiion, the Philippines; 6) the Salton Sea and Heber geothermal fields of southern California; and 7) the Dieng field in Central Java, Indonesia. We have analyzed the samples from all fields for REE except the last two. Our results indicate that measurement of the REE content of geothermal fluids can result in a wealth of information about water-rock interactions in geothermal systems that we have only just begun to explore. The results also continue to hold promise that such measurements may one day be a useful, routine tool for exploration for geothermal systems. However, additional developmental work wiU be necessary to realize the full power of the technique.